Dr. Yu will present two related works. 1)Sensing the direction of sounds gives animals clear evolutionary advantages as it helps to find mates, locate preys, and avoid predators. Small animals like crickets, flies, and geckos cannot rely on large interaural differences to localize sounds in an auditory scene. For decades, biologists, neuroscientists and physicists have tried to elucidate why these animals nonetheless exhibit excellent directional hearing. Recent studies have revealed an intricate angle-sensing mechanism that is completely different from those seen in large animals and relies on the coherent coupling of soundwaves in two ‘ears’. Here, we apply this mechanism to electromagnetic waves by demonstrating the effective use of a pair of electrically-isolated but optically-coupled photodetectors. Exploiting the anti-Hermitian interactions mediated through the continuum, resonant photodetectors can accurately differentiate incident angles using a subwavelength footprint. This works breaks the limitation of conventional photodetectors that only sense light intensity and lose all phase information in an incoherent detection process. 2)Wavelength determines the length scale of the cross section when electromagnetic waves are scattered by an electrically small object. The cross section diverges for resonant scattering, and diminishes for non-resonant scattering, when wavelength approaches infinity. This scattering law explains the color of the sky as well as the strength of a mobile phone signal. We show that such wavelength scaling comes from free space’s conical dispersion at zero frequency. Emerging Weyl systems, offering similar dispersion at non-zero frequencies, lead to new laws of electromagnetic scattering that allow cross sections to be decoupled from the wavelength limit. Diverging and diminishing cross sections can be realized at any target wavelength in a Weyl system, providing unprecedented ability to tailor the strength of wave-matter interactions for radio-frequency and optical applications.

BIO:Zongfu Yu is an Assistant Professor in the Department of Electrical and Computer Engineering at the University of Wisconsin–Madison. His research focuses on photonics and its applications in energy conversion, imaging, and sensing. He is a recipient of Stanford Postdoc Research Award, the Dugald Jackson Faculty Scholar Award, and DARPA Young Faculty Award. He has authored and co-authored over 100 peer-reviewed papers with a total citation over 10,000. He received his Ph.D. in applied physics and M.S. in management science and engineering, both from Stanford University, and a B.S. degree in physics from the University of Science and Technology of China.